I've been reading about the bombing and I don't really understand what lead to it. I know there was a civil war going on in Spain, but why would Hitler even get involved with the conflict? How much of the bombing was coordinated between Hitler and Franco?
It is incredibly likely neither leader knew about the actual raid until after it happened. From what I understand Guernica was along a series of roads that were being used by the Republicans to retreat and organize a defensive line against Franco's Nationalists.
The point of the raid was to destroy and degrade that transportation infrastructure and make the roads and bridges and all useless to help the Nationalist ground forces advance.
The Condor Legion, the German detachment sent to fight in Spain was under operational control of the Spanish, along with similar units from Italy. There were a great many international units fighting in Spain, on both sides.